I purchased maths and chemistry aqa a level packs of 3. Although yes, they were good unseen practice, there were MULTIPLE errors in both sets of papers. These were in terms of the theory, and also the spec (what formulas need to be memorised for aqa etc). I got in touch with the exam board where the designer of exams told me yes, their mistake was genuine. Upon emailing them, MME failed to give me an adequate refund and continued to deny the error, even with evidence from the exam board. This is what made me realise it's a money making business and they don't really care what's in the paper.